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<title>WebGL - Scene Graph - Solar System</title>
<link type="text/css" href="resources/webgl-tutorials.css" rel="stylesheet" />
</head>
<body>
<div class="description">
Simulating a solar system using a scene graph.
</div>
<canvas id="canvas"></canvas>
</body>
<!-- vertex shader -->
<script id="vertex-shader-3d" type="x-shader/x-vertex">
attribute vec4 a_position;
attribute vec4 a_color;

uniform mat4 u_matrix;

varying vec4 v_color;

void main() {
  // Multiply the position by the matrix.
  gl_Position = u_matrix * a_position;

  // Pass the color to the fragment shader.
  v_color = a_color;
}
</script>
<!-- fragment shader -->
<script id="fragment-shader-3d" type="x-shader/x-fragment">
precision mediump float;

// Passed in from the vertex shader.
varying vec4 v_color;

uniform vec4 u_colorMult;
uniform vec4 u_colorOffset;

void main() {
   gl_FragColor = v_color * u_colorMult + u_colorOffset;
}
</script>
<!--
for most samples webgl-utils only provides shader compiling/linking and
canvas resizing because why clutter the examples with code that's the same in every sample.
See https://webglfundamentals.org/webgl/lessons/webgl-boilerplate.html
and https://webglfundamentals.org/webgl/lessons/webgl-resizing-the-canvas.html
for webgl-utils, m3, m4, and webgl-lessons-ui.
-->
<script src="resources/webgl-utils.js"></script>
<script src="resources/m4.js"></script>
<script src="resources/primitives.js"></script>
<script>
"use strict";

   var Node = function() {
     this.children = [];
     this.localMatrix = m4.identity();
     this.worldMatrix = m4.identity();
   };

   Node.prototype.setParent = function(parent) {
     // remove us from our parent
     if (this.parent) {
       var ndx = this.parent.children.indexOf(this);
       if (ndx >= 0) {
         this.parent.children.splice(ndx, 1);
       }
     }

     // Add us to our new parent
     if (parent) {
       parent.children.push(this);
     }
     this.parent = parent;
   };

   Node.prototype.updateWorldMatrix = function(parentWorldMatrix) {
     if (parentWorldMatrix) {
       // a matrix was passed in so do the math
       m4.multiply(parentWorldMatrix, this.localMatrix, this.worldMatrix);
     } else {
       // no matrix was passed in so just copy local to world
       m4.copy(this.localMatrix, this.worldMatrix);
     }

     // now process all the children
     var worldMatrix = this.worldMatrix;
     this.children.forEach(function(child) {
       child.updateWorldMatrix(worldMatrix);
     });
   };



function main() {
  // Get A WebGL context
  /** @type {HTMLCanvasElement} */
  var canvas = document.querySelector("#canvas");
  var gl = canvas.getContext("webgl");
  if (!gl) {
    return;
  }

  // creates buffers with position, normal, texcoord, and vertex color
  // data for primitives by calling gl.createBuffer, gl.bindBuffer,
  // and gl.bufferData
  const sphereBufferInfo = primitives.createSphereWithVertexColorsBufferInfo(gl, 10, 12, 6);

  // setup GLSL program
  var programInfo = webglUtils.createProgramInfo(gl, ["vertex-shader-3d", "fragment-shader-3d"]);

  function degToRad(d) {
    return d * Math.PI / 180;
  }

  function rand(min, max) {
    return Math.random() * (max - min) + min;
  }

  function emod(x, n) {
    return x >= 0 ? (x % n) : ((n - (-x % n)) % n);
  }


  var cameraAngleRadians = degToRad(0);
  var fieldOfViewRadians = degToRad(60);
  var cameraHeight = 50;

  var objectsToDraw = [];
  var objects = [];

  // Let's make all the nodes
  var solarSystemNode = new Node();
  var earthOrbitNode = new Node();
  earthOrbitNode.localMatrix = m4.translation(100, 0, 0);  // earth orbit 100 units from the sun
  var moonOrbitNode = new Node();
  moonOrbitNode.localMatrix = m4.translation(30, 0, 0);  // moon 30 units from the earth

  var sunNode = new Node();
  sunNode.localMatrix = m4.scaling(5, 5, 5);  // sun a the center
  sunNode.drawInfo = {
    uniforms: {
      u_colorOffset: [0.6, 0.6, 0, 1], // yellow
      u_colorMult:   [0.4, 0.4, 0, 1],
    },
    programInfo: programInfo,
    bufferInfo: sphereBufferInfo,
  };

  var earthNode = new Node();
  earthNode.localMatrix = m4.scaling(2, 2, 2);   // make the earth twice as large
  earthNode.drawInfo = {
    uniforms: {
      u_colorOffset: [0.2, 0.5, 0.8, 1],  // blue-green
      u_colorMult:   [0.8, 0.5, 0.2, 1],
    },
    programInfo: programInfo,
    bufferInfo: sphereBufferInfo,
  };

  var moonNode = new Node();
  moonNode.localMatrix = m4.scaling(0.4, 0.4, 0.4);
  moonNode.drawInfo = {
    uniforms: {
      u_colorOffset: [0.6, 0.6, 0.6, 1],  // gray
      u_colorMult:   [0.1, 0.1, 0.1, 1],
    },
    programInfo: programInfo,
    bufferInfo: sphereBufferInfo,
  };


  // connect the celetial objects
  sunNode.setParent(solarSystemNode);
  earthOrbitNode.setParent(solarSystemNode);
  earthNode.setParent(earthOrbitNode);
  moonOrbitNode.setParent(earthOrbitNode);
  moonNode.setParent(moonOrbitNode);

  var objects = [
    sunNode,
    earthNode,
    moonNode,
  ];

  var objectsToDraw = [
    sunNode.drawInfo,
    earthNode.drawInfo,
    moonNode.drawInfo,
  ];

  requestAnimationFrame(drawScene);

  // Draw the scene.
  function drawScene(time) {
    time *= 0.0005;

    webglUtils.resizeCanvasToDisplaySize(gl.canvas);

    // Tell WebGL how to convert from clip space to pixels
    gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

    gl.enable(gl.CULL_FACE);
    gl.enable(gl.DEPTH_TEST);

    // Clear the canvas AND the depth buffer.
    gl.clearColor(0, 0, 0, 1);
    gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

    // Compute the projection matrix
    var aspect = gl.canvas.clientWidth / gl.canvas.clientHeight;
    var projectionMatrix =
        m4.perspective(fieldOfViewRadians, aspect, 1, 2000);

    // Compute the camera's matrix using look at.
    var cameraPosition = [0, -200, 0];
    var target = [0, 0, 0];
    var up = [0, 0, 1];
    var cameraMatrix = m4.lookAt(cameraPosition, target, up);

    // Make a view matrix from the camera matrix.
    var viewMatrix = m4.inverse(cameraMatrix);

    var viewProjectionMatrix = m4.multiply(projectionMatrix, viewMatrix);

    // update the local matrices for each object.
    m4.multiply(m4.yRotation(0.01), earthOrbitNode.localMatrix, earthOrbitNode.localMatrix);
    m4.multiply(m4.yRotation(0.01), moonOrbitNode.localMatrix, moonOrbitNode.localMatrix);
    // spin the earth
    m4.multiply(m4.yRotation(0.05), earthNode.localMatrix, earthNode.localMatrix);
    // spin the moon
    m4.multiply(m4.yRotation(-0.01), moonNode.localMatrix, moonNode.localMatrix);

    // Update all world matrices in the scene graph
    solarSystemNode.updateWorldMatrix();

    // Compute all the matrices for rendering
    objects.forEach(function(object) {
      object.drawInfo.uniforms.u_matrix = m4.multiply(viewProjectionMatrix, object.worldMatrix);
    });

    // ------ Draw the objects --------

    var lastUsedProgramInfo = null;
    var lastUsedBufferInfo = null;

    objectsToDraw.forEach(function(object) {
      var programInfo = object.programInfo;
      var bufferInfo = object.bufferInfo;
      var bindBuffers = false;

      if (programInfo !== lastUsedProgramInfo) {
        lastUsedProgramInfo = programInfo;
        gl.useProgram(programInfo.program);

        // We have to rebind buffers when changing programs because we
        // only bind buffers the program uses. So if 2 programs use the same
        // bufferInfo but the 1st one uses only positions the when the
        // we switch to the 2nd one some of the attributes will not be on.
        bindBuffers = true;
      }

      // Setup all the needed attributes.
      if (bindBuffers || bufferInfo !== lastUsedBufferInfo) {
        lastUsedBufferInfo = bufferInfo;
        webglUtils.setBuffersAndAttributes(gl, programInfo, bufferInfo);
      }

      // Set the uniforms.
      webglUtils.setUniforms(programInfo, object.uniforms);

      // Draw
      gl.drawArrays(gl.TRIANGLES, 0, bufferInfo.numElements);
    });

    requestAnimationFrame(drawScene);
  }
}

main();
</script>
</html>
